To busby: If you are on the latest firmware MyBookLive 02.10.09-124 : Core F/W - there is a new option to rebuild the WD2Go Database (which is also used by WD Photos).

Open the MBL UI page - click on remote access tab - Go down to bottom of page and expand the advanced heading. In there you will find a rebuild button for the WD2Go database. Click on rebuild - and allow the db to rebuild. This should remove your deleted folder.

You may also want to remove your mobile device from remote access and re-add it after the rebuild completes - but check to see if the rebuild alone resolves your issue first.